Spectro-interferometric observation of SW Vir

Our aim is to probe the physical properties of the outer atmosphere with spatially resolved data in individual molecular and atomic lines. We observed SW Vir in the spectral window between 2.28 and 2.31 micron with the near-infrared interferometric instrument AMBER at ESO's Very Large Telescope Interferometer (VLTI).

Thanks to AMBER's high spatial resolution and high spectral resolution of 12000, the atmosphere of SW Vir has been spatially resolved not only in strong CO first overtone lines but also in weak molecular and atomic lines of H_2_O, CN, HF, Ti, Fe, Mg, and Ca. While the uniform-disk diameter of the star is 16.23+/-0.20mas in the continuum, it increases up to 22-24mas in the CO lines. Comparison with the MARCS photospheric models reveals that the star appears larger than predicted by the hydrostatic models not only in the CO lines but also even in the weak molecular and atomic lines.